So, I made it up. But why shouldn’t there be both a publication and a trade show dedicated to the essentials of printed circuit board ejector systems? In the design and execution of front panel mounting systems, ejectors are the true core technology. There are expos for everything else – and we are continually bombarded by trade show announcements of every description. Earlier this month the Sweets and Snacks Expo made its annual pilgrimage to Chicago while my personal favorite, the Rocky Mountain Reptile Expo arrives in Denver this August.
Even though at first glance this looks like a tongue-in-cheek spoof, I’m more serious than you think. Auto shows have been around for over 100 years, mostly to stimulate sales of the new models, but also to tantalize the senses with visionary styles and technical gymnastics expected from concept cars yet a few years away. Front Panel Ejector Systems deserve their shot, too. After all, they have served as a mainstay of chassis product development for over 50 years.
To wit, below is a partial drawing from a 1960 ejector patent, assigned to South Chester Corporation (the parent of Southco).
Now that you are my captive audience – we’re set to go. You’re all checked in and you have your lanyard ID, so let’s see what’s inside the first of six sessions:
Ejector Expo Session 1 - History
In session one there’s a bit more history. Without the lever, ejector designs would have been clumsy at best, so we first pay homage to the renowned promoter of the lever’s virtue, Archimedes.
The Lever Principle
“Give me a lever long enough and a place
to stand and I will move the entire earth.”
Archimedes (c.287-212 B.C.)
Secondly, we give a nod to the guys at Reeves Instruments for a 1953 solution embedded in the circuit boards of an analog computer chassis. This patent perhaps best captures the original justification for levered ejection.
[T]he importance of this [feature] will be appreciated when it is realized that the circuits of an electronic computer, for the solution of a given problem, involve over 500 connections and may take several days to make the necessary connections for the solution of one particular problem.
Patent 2,647,244, Reeves Instruments, July 1953
Ejector Expo Session 2 - How much leverage is enough?
An inject/eject system design must be capable of the leverage required to insert and extract the PCB from its backplane connector(s). The durability specification for the number of insertion and extraction cycles is typically 500, dictating a degree of strength and operational reliability commensurate with a range of backplane forces. In relatively small PCB’s like 6U VPX, the forces may be 75 to 100 lbs. while a large custom circuit pack, of the varieties used by Cisco, Juniper, Alcatel, and others, could easily reach 200-400 lbs. depending on the connector pin counts. In the latter cases it is essential to create specific ejector designs, often in extruded aluminum or heavy gage sheet metal, perhaps in die cast alloys, to satisfy force requirements as well as optimal ergonomic form. If the ergonomics are marginal, the fundamental utility and reliability will suffer.
Thoughtful mechanical design, and related tolerances to the chassis interface, will ensure proper preset positions for the inject cycle and smart, hand / finger access for the eject cycle.
Ejector Expo Session 3 - A Leading Role in Front Panel Appearance
The session on appearance runs in tandem with the one on graphic design. The presenters here are insistent that providing an integrated Front Panel and Ejector treatment distinguishes the customer’s product in the marketplace, and will have a positive influence on sales.
With regard to the “Validation of Perception”, there is an implied product requirement to present the combined face of a high-end, customized system where its value mirrors the excitement of its performance and the ruggedness of its field deployment.
The use of powder coated, custom colored handles and complementary, reverse printed, polycarbonate overlays in recessed galleries, work together here. The ‘Wow’ factor generated is often combined with tasteful treatments of the respective customer’s corporate identity.
Ejector Expo Session 4 - Negotiating Style with Shielding Overhead
This session examines two different EMC shielding insurance policies.
- External Ejection – where the inject/eject “claw” is on the outside of the Front Panel.
- Internal Ejection – where the inject/eject “claw” is on the inside the Front Panel
No surprise that the external ejector is more EMC Compliance friendly. It’s a little like the twist toggle on an old shoe polish can – the can is sealed up tight but can be pried open easily from an external lever. There are no mechanical interface orifices from which EMI can escape in an external ejector system. With the ever-increasing clock rates being generated from components within the circuit packs, this approach continues to gain favor. Often the eject levers are spring loaded against stops to create the proper bias for insertion alignment.
Internal ejector systems can be easier to design, and are generally less expensive to manufacture. However, sealing up the ‘slot antennae’ which surround the mechanics as they pass through the panel, can pose problems with higher processor speeds. Fortunately there are a variety of self-adhesive shielding foams that can be die-cut and assembled to provide leakage seals around those transitional openings.
Recommended takeaways from this session:
- Those product designers that are able to work closely with a Front Panel manufacturer, optimizing ejector configurations within their front panel assemblies, will experience fewer prototype and startup headaches.
- Commitments to Industrial Design-driven ejector solutions are best delayed until the specific fundamental ejector concepts are demonstrated and solidified.
|In case you didn’t notice, we’ve just had our lunch break and are back for the afternoon sessions.|
Ejector Expo Session 5 - Hot Swap
So we’ve discussed the means to pry circuit packs from their backplanes and reinsert them with reasonable effort and with confidence in the accuracy of their placement. The desire to replace individual circuit packs without time consuming system shut downs is a no-brainer. The notion of hot swap, a designed-in capability to safely power down, extract, and replace a single blade, is becoming a standard feature with an obvious financial benefit in down time avoidance.
In order to effect the graceful power down prior to extraction, a switch is mechanically interlocked to the ejector itself, or more often to an interposer or slide thus preventing accidental or premature actuation of the ejectors. By requiring a separate motion to actuate the hot swap switch prior to allowing movement of the ejectors, an additional window of power down time is achieved. See the external ejector example above.
Ejector Expo Session 6 – The Economics
This session first lays out the value proposition for ejectors which are available for the many standards. In the IEEE 1101.10 family – cPCI, VME, VPX, VXS, and their variants – there are at least seven manufacturers of that family of inject/eject hot swap capable handles. Construction and appearance, although similar, are distinguished by a menu of features. These range from metal jaws, all metal handles, short handles, long handles, and colored handles to single width, double and triple width, with various ergonomic release and latching schemes. Equally as varied are the permissive prices for this range of products. Likewise, the AMC, MicroTCA, and ATCA handles have similar breadth in their sourcing as well as their value proposition feature set.
In the Custom Ejector world, the economies are driven by both design execution and the manufacturing volumes. Not surprisingly, a set of ejectors with a hot swap feature can be produced for startup in traditional and rapid prototype modalities – machining of net shape aluminum extrusions or rapid prototype castings with finish machining. With forethought on the part of a design / manufacturing partnership, they can successfully migrate painlessly into a high volume, low amortized cost solution.
CBT Technology has been producing and developing Front Panels with custom ejector solutions for over 25 years. Additionally they are well positioned by supporting a complete line of the standard inject/eject front panel solutions from both captive and open source manufacturers.
Well, that finishes up this virtual Ejector Expo and I thank each and every one of you for joining me. My hope is that you can now view ejector systems as the singular most essential element of Front Panel Solutions and that cooperative design partnerships are the key to successful, timely implementations.
Let’s face it – A Front Panel assembly without Ejectors is just another Filler Panel.
I can see it – the next issue of FILLER PANEL MONTHLY and the 2013 Las Vegas Slot Blocker Show
Hope to see you all in August!